1. Field of the Invention
The present invention relates to a high power light-emitting diode (HP LED) package, which includes a predetermined substrate having a protruding portion (hereinafter, referred to as a ‘beacon’) to improve heat release performance and increase the lifetime of the HP LED, by enabling direct mounting of the IHP LED, which generates heat, on a metal or non-metal substrate having high heat conductivity, and eliminating wiring, which functions to apply signals and electric power, from a heat transfer path.
2. Description of the Related Art
Generally, an LED, which is formed of a Group III-V or II-VI compound semiconductor, including GaAs, AlGaAs, GaN, InGaN or AlGaInP, is a diode-able to emit its excess energy in the form of a photon upon coupling and recombination between electrons injected into an N layer and holes of a P layer through application of current. For example, there are a red LED using GaAsP, a green LED using GaP, a blue LED using a double hetero structure of InGaN/AlGaN, etc. Further, attempts to realize a white LED, including appropriately. combining RGB (Red, Green, Blue) LEDs and applying phosphor to the blue LED, have been made.
Although LEDs have been used as lamp type indicators to date, their application to backlight units of flat panel displays, general lighting fixtures, and automobiles, which can. be realized by increasing the luminance and light emission thereof, is under study.
Typically, an HP LED requires high luminance, a long lifetime and superior reliability, and its performance and properties are determined by color temperatures, luminance, and luminance intensities. To increase luminous efficiency, methods of increasing the degree of crystal growth of an active layer, an electron-injecting (N) layer and a hole-injecting (P) layer of the LED are first proposed. Additionally, the above performance of the LED is determined by a structure that efficiently releases heat, a controllable wiring structure, and a bonding process for connection of the diode to the wiring substrate. In realizing high light emission properties of the HP LED, the characteristics of the compound semiconductor material greatly affect the HP LED, thus various limitations are imposed on manufacturing such an LED. Hence, research into LED package structures is actively being carried out.
Moreover, the HP LED should have improved heat release properties, in order to obtain a long lifetime and high reliability. To this end, a surface mounted device (SMD) suitable for increasing heat release properties has been developed as shown in FIGS. 3, 4 and 5.
Referring to FIGS. 3, 4 and 5, a flip-chip bonding or wire-bonding type HP LED 301a, 401a, 501a is attached to the upper surface of a heat slug 301c, 401d, 501d using a solder or an adhesive having improved heat conductivity 301b, 401b, 501b, after which the heat slug is attached to the upper surface of a wiring substrate using an adhesive having improved heat conductivity 301d, 401e, 501f. The wiring substrate includes a wiring layer 303, 402, 502 and an insulating layer 302, 403, 503 to electrically insulate the wiring layer from a heat spreader 304, 404, 504 made of aluminum (Al), copper (Cu), or ceramic (SiC, AlN or AlSiC) having high heat conductivity, each of which is sequentially laminated on the heat spreader. For bonding the wiring substrate with the heat slug 301c, 401d, 501d, solder or adhesive having improved heat conductivity 301d, 401e, 501f is used. In addition, a reflection cup 401d is provided to improve the angle of light distribution from the LED and the luminance of the LED. The heat generated from the LED is simultaneously released through three pathways, that is, conduction, convection and radiation. The heat is transferred through the media connected to the LED, sequentially from the medium having the highest heat conductivity to the medium having the lowest heat conductivity. Therefore, heat is transferred through conduction into the package, formed of a conductor and a semiconductor having high heat conductivity, in an amount greater than that transferred through convection and radiation out of the package exposed to air having heat conductivity of 0.024 W/mK (@° C.). From this, it should be noted that heat is preferably released from the package through conduction. With respect to heat release, the principle of the conduction for transferring heat to a predetermined region obeys a Fourier's law. A heat transfer rate is represented by Equation 1 below:
                    q        =                              -            k                    ⁢                                          ⁢                      A            ⁡                          (                                                ⅆ                  T                                                  ⅆ                  x                                            )                                                          Equation        ⁢                                  ⁢        1            
In Equation 1, q shows a heat transfer rate and is in proportion to heat conductivity k of a medium to be conducted, an area A thereof, and a change of temperature to distance dT/dx.
In the case where the HP LED coexists with a material having low heat conductivity in a small space on a heat transfer-path, its heat transfer rate is decreased. Further, thermal fatigue accumulates in the HP LED. When electrons are injected into the N layer of the HP LED, a scattering phenomenon occurs due to collisions of lattice atoms of the semiconductor. The higher the temperature, the more the lattice scattering. Thereby, electron mobility and. forward voltage and current are decreased, and less coupling and recombination with the holes result, thus the luminous efficiency of the HP LED may be lowered and the HP LED may malfunction. The individual structures shown in FIGS. 3, 4 and 5 include at least three barrier layers having low heat conductivity upon transfer of heat from the HP LED to the heat spreader 304, 404, 504. As seen in FIGS. 3, 4 and 5, the first barrier layer is the adhesive 301b, 401b, 501b having improved heat conductivity used to attach. the HP LED 301a, 401a, 501a to the heat slug 301c, 401d, 501d, and has heat conductivity of 0.3˜1 W/mK and a thickness. of 50˜150 μm. The second barrier layer is the solder or adhesive 301d, 40le, 501f used to attach the heat slug to the wiring. layer 303, 402, 502 of the wiring substrate, and has heat conductivity of 37˜55 W/mK depending on the proportions of tin (Sn) and lead (Pb) when using solder, and heat conductivity of 0.3˜1 W/mK when using adhesive having improved heat conductivity, with a thickness of 50˜100 μm. The third barrier layer is the insulating layer 302, 403, 503 of the wiring substrate, and has heat conductivity of 0.35˜23 W/mK and a thickness of 50 μm or more. Even if the types of HP LED mounted in FIGS. 3, 4 and 5 are the same, the junction temperature of the HP LED may be greatly increased by the kinds, thicknesses and structures of heat transfer media. In particular, as the number of junction layers having low heat conductivity is increased, these layers function as heat barriers, thus increasing thermal fatigue. Consequently, the HP LED becomes unreliable in view of long-term operation and performance.